The present invention relates to power amplifiers for use in wireless communication systems.
In wireless communication systems, digital signals are transmitted in order to facilitate communication. The signals used in these systems often are phase and amplitude modulated to encode transmitted information. Power amplifiers are used to amplify these low-power, modulated signals prior to transmission. Existing power amplifiers in wireless communication systems suffer from several problems, such as non-linearity and inefficiency issues. Examples of these conventional power amplifiers are linear amplification with nonlinear components (Linc) amplifiers and envelope elimination and restoration (EER) amplifiers.
Linc amplifier systems decompose an input signal into two phase-modulated vector signals with constant amplitudes. Power amplifiers amplify the vectors and a power combiner combines them to generate a power-amplified output signal. However, as the difference between the phases of the vector signals increase, the power combiner wastes more power and becomes increasingly inefficient.
EER amplifier systems split an input signal into a variable amplitude modulated signal and a phase modulated signal with a constant amplitude. A power amplifier amplifies the phase modulated signal. A modulator circuit modulates the supply voltage of the power amplifier based on the amplitude modulate signal. Ideally, the output signal would be an amplified version of the input signal. Although the EER system is somewhat efficient, its linearity is significantly limited by the bandwidth limitations of its modulator circuit.
As the demand for faster and more efficient mobile communications devices continues to increase, the demand for radio frequency (RF) transmitters supporting higher data transmission rates also has increased. In existing systems, these higher data transmission rates have been implemented by increasing the bandwidth of data signals transmitted by the RF transmitters. To support these wider bandwidths, the bandwidth requirements for power amplifiers used in RF transmitters have also been increased. Increased bandwidth problems further compound non-linearity and inefficiency problems, therefore existing power amplifier architectures are becoming obsolete. Thus, there is a need in for wide bandwidth, highly efficient and linear power amplifiers for use in wireless communication systems.